1. Field of the Invention
The invention relates to a wheel truck, and more particularly to a railroad freight car wheel truck.
2. Description of the Related Art
As a critical part of a freight car, a typical railroad freight car wheel truck includes two side frame assemblies and a bolster assembly. Journal-box guides disposed on two ends of the side frame assembly are fixed on a front wheel pair and a rear wheel pair via roller bearing adapters and bearing assemblies, respectively. Each end of the bolster assembly is mounted in a central square box of the side frame assembly via a spring suspension device. The spring suspension device includes a bearing spring unit in the center, two damping springs on both sides, and two wedges each of which is disposed on a top of each damping spring. A vertical primary friction surface and an inclined secondary friction surface of the wedge contact with a column surface of the side frame assembly and an inclined surface of the bolster assembly, respectively. The bearing spring units, the damping springs, together with the corresponding wedges bear the load of the bolster assembly.
On each end of the upper surface of the bolster assembly a side pedestal is arranged. The side pedestals and a center plate of the bolster assembly bear the load of the freight car. The wheel truck further includes a basic braking device for braking.
The wheel truck, as described above, is advantageous in its simple structure, uniform distribution of the load, low cost in production and maintenance However, the connection between the bolster assembly and the side frame assembly is loose and the diamond resistant rigidity is low, which cannot resist the violent shaking between the bolster assembly and the side frame assembly. And when the wheel truck runs on a curved rail track, the attack angle between the wheel pairs and the rail enlarges, thereby resulting in damages on the wheel and the rail.
Particularly, the wedge of the spring suspension device has a relative larger apex angle, that is, the angel between the secondary friction surface and a vertical plane is about 35-70°. Thus, the diamond resistant rigidity is highly limited. When the bolster assembly moves downwards relative to the side frame assembly, a vertical force component of a force from the inclined surface to the wedge is larger than a sum of vertical force components of the friction produced on the primary friction surface of the wedge and the friction produce on the secondary friction surface of the wedge, so that the wedge moves downwards, and the vertical distance between the bolster assembly and the side frame assembly becomes smaller, thereby resulting in relative rotation between the bolster assembly and the side frame assembly, as well as diamond deformation. In such a condition, the critical speed of the wheel truck is low, which limits the running speed and running performance of the freight car, and cannot meet the requirement of the speed-raising freight car.
To solve the above problems, the existing speed-raising trains employs a cross supporting device or a spring plank between two side frame assemblies for improving the diamond resistant rigidity of the conventional railroad freight car wheel truck. The problem is that, such a cross supporting device or spring plank has a complicated structure, heavy weight, and high production and maintenance costs. Thus, it is very significant to improve the conventional railroad freight car wheel truck and to design a wheel truck that has a high diamond resistant rigidity and a superb dynamic performance.